The Convention Conundrum - S7-E14
Character mistake: On Sheldon's board of possible attendees for his convention he has misspelled Ian McKellen - with 'an' at the end.
The Proton Displacement - S7-E7
Character mistake: When Raj shows Penny, Amy, and Bernadette how to make jewelry, Penny keeps having trouble with the glue and gets it all over her fingers. However, in Season 2, episode 5, she has no trouble at all with the glue when making 1000 Penny Blossoms.
Answer: Because Raj's selective mutism seems to be caused by women that Raj sees (on some sort of conscious or subconscious level) as a potential sexual partner. An attribute that wouldn't apply to either his sister or mother.